1. Field of the Invention
The present invention relates to an image forming apparatus capable of forming a document image having images and (or) characters on the surface of a medium by causing ink to be sprayed onto the corresponding medium.
2. Description of the Related Art
An image forming apparatus for forming a document image having images and (or) characters on the surface of a medium by causing ink to be sprayed onto the corresponding medium such as a printing paper includes medium feeding rollers for feeding the above-described medium and a carrier that reciprocates while holding ink cartridges in which ink is sealed.
The above-described image forming apparatus includes a printing area, into which the above-described medium is fed, for printing a document image composed of images and (or) characters and a maintenance area in which the carrier having ink cartridges mounted thereon is disposed while the above-described printing is not carried out.
The ink cartridges mounted on the above-described carrier has nozzles for discharging the above-described ink. A black ink cartridge in which a black ink for black printing is sealed and a color ink cartridge in which a cyan ink, magenta ink, and yellow ink (so-called “color inks”) for color printing are, respectively, divided and sealed are mounted on the above-described carrier adjacent to each other.
The above-described carrier and ink cartridges move to the above-described maintenance area after printing is finished. Further, where no operation is carried out for a prescribed period of time, the carrier and ink cartridges move to the home positions secured in the maintenance area and stand by therein where the main power source of the above-described image forming apparatus is turned off. At this time, the nozzles of the respective ink cartridges are capped in order to prevent ink from drying up in the respective nozzles. The caps are fixed on a movable member called a “sled,” and the corresponding sled is elevated from downward of the carrier in line with the movement of the above-described carrier to the home position, wherein the above-described caps are placed on the respective nozzles.
Also, in printing, excessive ink adhered to the nozzles and to the vicinity thereof is wiped off by the nozzle wiper secured at the above-described sled immediately after commencing an operation, and the above-described carrier and the above-described ink cartridges, which are disposed at the above-described home position, move to the printing area. Since excessive ink adhered to the nozzles and to the vicinity thereof is wiped off by the nozzle wiper, it is possible to increase the accuracy of printing on the above-described medium, and it is possible to lessen printing stains.
However, there is a case where it is insufficient that only the excessive ink adhered to the above-described nozzles and the vicinity thereof is wiped off by the nozzle wiper. In such a case, a type has been proposed, which carries out preliminary discharge, that is, discharges ink through the nozzles of the above-described ink cartridges at a position (that is, a position in which the nozzles and caps are not lined up straightly, hereinafter called a “preliminary discharge position”) where the above-described carrier and ink cartridges slightly moved from the above-described home position.
In a case of an image forming apparatus in which the above-described preliminary discharge is carried out, there are many cases where portions onto which ink is applied by the preliminary discharge of the above-described sled are provided with ink-release ports in order to lessen the corresponding ink is adhered to the sled.
However, although color inks having lower viscosity flow out by repeating the preliminary discharge at the above-described preliminary discharge position, black ink having high viscosity is accumulated downward of the corresponding preliminary discharge position, and is gradually adhered to the above-described sled and (or) carrier, thereby hindering movements of the corresponding sled and (or) carrier.
Therefore, such a type has been proposed, which an ink receiving cup to receive ink discharged from the above-described preliminary discharge is disposed at a position downward of the ink release ports of the above-described sled when the above-described ink cartridges carry out preliminary discharge at the above-described preliminary discharge position.
The ink receiving cup is saucer-shaped which is circular in its plan view, and slightly turns whenever preliminary discharge is carried out, wherein preliminary discharge is carried out at a position slightly shifted from the previous preliminary discharge position in respective preliminary discharge. Thereby, since the preliminary discharge is carried out at different positions, it is possible to lessen accumulation of black ink.
Some rotation mechanisms are available with respect to the above-described ink receiving cup, in one of which the ink receiving cup is rotated by a motor, and in another of which serrated projections and recesses are formed on the outer circumferential face of the above-described ink receiving cup, and the projections and recesses are pressed in one direction by a rotating member secured on the underside of the above-described sled, as disclosed in JP-A-2001-293887.
However, it is possible to improve the printing accuracy without hindering movements of the above-described sled and carrier due to accumulation of the above-described black ink by carrying out preliminary discharge of the corresponding black ink. The above-described preliminary discharge is carried out for the nozzle of a color ink cartridge, wherein the above-described ink receiving cups are filled with color ink by executing the preliminary discharge several times. Therefore, if the above-described preliminary discharge is carried out in a state where the above-described ink receiving cups are filled with color ink, the above-described black ink and (or) the above-described color inks are discharged into the color inks in the above-described ink receiving cups. Therefore, color inks are splattered.
The splattered color ink is adhered to the nozzles of the black ink cartridge and color ink cartridge and to the vicinity thereof, resulting in such troubles, which lower the printing accuracy and form printing stains on the above-described medium.